"This is addressed to the young men who bear arms against their own nations and destroy both country and countrymen," the document begins. "You have abandoned all values and made enemies of the world. We call on you to pause, reflect and heed this counsel for the sake of all who want good for our community."

Syeed says bin Bayyah attacks ISIS on two fronts: its lack of authority and its behavior.

First, ISIS is claiming authority when it has no legal justification for doing so.

Second, bin Bayyah takes issue with "the way they are using that authority, their behavior, their dealings, killing the minorities, molesting women and destroying properties and so on," Syeed says. "So that is totally outside any understanding of Islam."

"So it is the authority and use of the authority that he has legally shown is totally un-Islamic," Syeed says.

Syeed also characterizes the problem of ISIS as "a global phenomenon."

"They seem to be technologically savvy," Syeed says, "so they have a global outreach." As such, people can be easily misled by slogans, names and some terminology.